Best to use an objective-c parsing library.
This article has a good run down of some of the available ones:
http://www.raywenderlich.com/553/how-to-chose-the-best-xml-parser-for-your-iphone-project
Also, this page has full code samples using one of the libraries:
http://www.raywenderlich.com/725/how-to-read-and-write-xml-documents-with-gdataxml